In a communication system a communication network is provided, which can link together two communication terminals so that the terminals can send information to each other in a call or other communication event. Information may include speech, text, images or video.
Modern communication systems are based on the transmission of digital signals. Analogue information such as speech is input into an analogue to digital converter at the transmitter of one terminal and converted into a digital signal. The digital signal is then encoded and placed in data packets for transmission over a channel to the receiver of another terminal.
Each data packet includes a header portion and a payload portion. The header portion of the data packet contains data for transmitting and processing the data packet. This information may include an identification number and source address that uniquely identifies the packet, a header checksum used to detect processing errors and the destination address. The payload portion of the data packet includes information from the digital signal intended for transmission. This information may be included in the payload as encoded frames such as voice frames, wherein each frame represents a portion of the analogue signal.
Degradations in the channel on which the information is sent will affect the information received at the receiver. Degradations in the channel can cause changes in the packet sequence, delay the arrival of some packets at the receiver and cause the loss of other packets. The degradations may be caused by channel imperfections, noise and overload in the channel. This ultimately results in a reduction of the quality of the signal output by the receiving terminal.
One type of communication network suitable for transmitting digital information is the internet. Protocols which are used to carry voice signals over an Internet Protocol network are commonly referred to as Voice over IP (VoIP). VoIP is the routing of voice conversations over the Internet or through any other IP-based network.
One example of a communication system to use VoIP is a peer to peer communication system, in which a plurality of end users can be connected for communication purposes via a communications structure such as the internet. A peer to peer network may also use other protocols to facilitate the transfer of other data such as text images or video. The communications structure is substantially decentralised with regard to communication route switching therein for connecting the end users. That is, the end users can establish their own communication routes through the structure based on exchange of one or more authorisation certificates (user identity certificates—UIC) to acquire access to the structure. The structure includes an administration arrangement issuing the certificates to the end users. Such a communication system is described in WO 2005/009019.
“Packet Voice Rate Adaptation through Perceptual Frame Discarding” by Steffen Praestholm et. al. discloses a method for discarding frames in an encoding system. The method disclosed makes use of an objective measure of speech quality (PESQ) to evaluate the effect of a discard. This is done be evaluating the objective difference according to this measure of the decoded frame and a packet loss concealment—replacement of this frame. The audio quality resulting from this method is limited by the limitations of the packet loss concealment method used. Further, the evaluation of each frame to identify which frames to discard is computational complex because of the closed loop evaluation of an objective measure of speech quality.
The prior art uses complex computational methods to achieve limited improvements in the quality of transmitted data. This increases processing overheads including hardware resources and processing time.
It is therefore an aim of the present invention to improve the perceived quality of the received signal. It is a further aim of the present invention to provide a method of improving the quality of the received signal without the use of complex computational methods.